JPS627166A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device having high reliability by forming a silicic nitride film in contact with a semiconductor substrate, and patterning by an electron beam drawing method or an X-ray exposing method. CONSTITUTION:After an element separating insulating film 2 is formed on the surface of a P-type Si substrate 1, a gate insulating film 3 is formed. In other words, a silicon wafer is etched, thermally oxidized, inserted into a diffusion furnace, thermally nitrided to form a silicic nitride film as a gate insulating film 3. Thereafter, a polysilicon gate 4 is formed, source and drain diffused layer 5 is formed by ion implanting to form an MOS transistor. Further, interlayer insulating films 6, 8 and aluminum wirings 7, 9 are formed to form an MOS type semiconductor device. The lithographic technique in use is all performed by an electron beam direct drawing method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing a semiconductor device using an electron beam direct writing method or an X-ray exposure method.

[Background of the invention]

Electron beam direct writing method and X-ray exposure method are effective means to replace ultraviolet exposure method in forming fine patterns of 1 μm or less. , Vac, S.
rn by S. Qkazaki et al. in ci, Technol, ) supra 1927 (1981).
-Electron-beam dir writing of MOS and analysis of overlay accuracy and line width accuracy J
ectwriting of n-MOS device
es and analysis of overlay
and 1inevidth accuracies
) is discussed in the paper entitled: As discussed in this document, there is a problem in that MOS transistors manufactured using the electron beam direct writing method have lower long-term reliability than MOS transistors manufactured using the ultraviolet exposure method. was there.

[Purpose of the invention]

An object of the present invention is to improve long-term reliability compared to the conventional technology. An object of the present invention is to provide a method for manufacturing a highly reliable semiconductor device using an electron beam direct writing method or an X-ray exposure method.

[Summary of the invention]

As MOSLSIs become more sophisticated and highly integrated, their gate dimensions are becoming smaller year by year. Along with this, MOSLS
In the production of I, the exposure method using ultraviolet rays has been replaced by an electron beam direct writing method or an X-ray exposure method that can resolve finer patterns. However, Mo8LSI using electron beam direct writing method or X-ray exposure method
The problem was that long-term reliability was lower than that of Mo5LSI using ultraviolet exposure. An example thereof will be explained using FIG. - The figure shows a given D for the lMo5 transistor.
It shows the time change of transmission and conductance g and m when C bias is applied. The MOS transistor has a channel length of 2 μm, a channel width of 15 μm, and an oxide film thickness of 20 nm. When applying a DC bias of 8 V to the drain, 4 V to the gate, and -3 V to the OV substrate to the source, and accelerating characteristic deterioration with a drain voltage higher than the general operating conditions, the deterioration rate of gm Δg m/ g m,
(gma is the gm value before application of DC stress). The straight line (a) in the figure is the experimental result of a MoS transistor manufactured using the electron beam direct writing method, and the true line (b) in the figure is the experimental result of the MoS transistor manufactured using the ultraviolet exposure method. From the same figure, it can be seen that when the electron beam direct writing method is used, the characteristic deterioration is three orders of magnitude faster and the long-term reliability is low. The reason for this is that a large amount of neutral traps are formed in the gate oxide film by the high-energy electron beam irradiated by the electron beam direct writing method, and hot carriers generated during transistor operation gradually become Sin, /S.
It is thought that this is trapped in a neutral trap in the gate oxide film near the i-interface, causing fluctuations in threshold voltage and deterioration in transfer conductance. Therefore, after conducting experiments with various oxide film qualities, it was newly discovered that when an oxynitride film obtained by thermally nitriding an oxide film is used as a gate insulating film, the time change in gm can be suppressed to a low level. Figure 1 shows an example of the results. Figure 1 (a) shows the case where a Mo8)-transistor with a conventional oxide film as the gate insulating film was formed by the electron beam direct writing method, and Figure 1 (b) shows the case of using oxynitride. M with film as gate insulating film
FIG. 2B shows the results of a DC stress test when an MOS transistor is formed using an oxynitride film as a gate insulating film and is formed using an electron beam direct writing method. The transistor specifications and DC stress conditions are the same as those described in FIG. Compared to those using conventional oxide films, those using oxynitride films have a lower g
It can be seen that the deterioration of m is small and the long-term reliability is excellent. When the elemental profile in the depth direction of the oxynitride film was investigated using Auger electron spectroscopy, nitrogen pile-up was observed at the SiO, /Si interface, and this nitrogen is thought to contribute to the stability of the interface properties. .

[Embodiments of the invention]

The first embodiment of the present invention will be described below with reference to FIG. This figure is a schematic cross-sectional view of the manufactured MoS transistor. In manufacturing the MOS transistor, conventional techniques are used except for the method of forming the gate insulating film.

After forming an element isolation insulating film 2 on the surface of a P-type Si substrate 1, a gate insulating film 3 was formed. The gate insulating film 3 was formed as follows. Silicon wafer HF:H,O=
After etching with a 1:10 etchant for 60 seconds and removing the etchant with pure water, it was immediately placed in a diffusion furnace to perform thermal oxidation. Thermal oxidation is at a temperature of 1000°C, and the incoming gas is o2:N
, = 1:1 for 25 minutes to form a thermal oxide film with a thickness of about 21 nm. Then HF:H,O=1:99
Etch the thermal oxide film for 20 seconds with the etchant.

After removing the etchant with pure water, it was immediately placed in a diffusion furnace and subjected to thermal nitriding.Thermal nitriding was carried out for 10 minutes at a temperature of 950°C and the inflow gas was NH3:3Q/win.
A 0 nm silicon oxynitride film was formed to serve as a gate insulating film. After that, a poly-Si gate 4 is formed, and source and drain diffusion layers 5 are formed by ion implantation to form a MOS.
Created a transistor. Furthermore, by forming interlayer insulating films 6, 8 and Afi wiring 7.9, an MO5 type semiconductor device having the structure shown in FIG. 3 was manufactured. All lithography techniques used in manufacturing were electron beam direct lithography. The accelerating voltage of the electron beam was 30 kV. The time change of gm due to DC stress of the MOS transistor formed with this pile is shown in FIG. 2 (b) above. The MOS transistor has a channel length of 2 μm and a channel width of 15 μm. Compared to the result of using a thermal oxide film as the gate insulating film, as shown in FIG. 2(a), the deterioration of gm is smaller and the long-term reliability is improved.

Next, a second example will be described. In this example,
A MO8O8 type semiconductor device having the structure shown in FIG. 3 was manufactured by the same manufacturing method as in the first example except that the X-ray exposure method was used as the lithography technique. In the X-ray exposure method, an electron beam excitation X-ray source is used as x and iam, and a 1Mo target is irradiated with a 20 kV electron beam.
Exposure was performed using the generated characteristic X-rays. M formed by this method
Line (b) in Figure 4 shows the time change in gm deterioration due to DC stress in an OS transistor. Line (a) in the same figure shows gm deterioration in a MoS transistor that uses a conventional thermal oxide film as the gate insulating film. There is.

By using this method, the deterioration of GM was reduced and long-term reliability was improved.

In addition, in the example, the channel length is 2 μm.

Although the description has been made using an NMOS transistor with a channel width of 15 μm, it goes without saying that the present invention is not limited to the size of the element or the materials of the substrate, wiring, etc.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to improve the reliability of an MO8 type semiconductor device manufactured using an electron beam direct writing method or an X-ray exposure method.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the effect of the present invention, FIG. 2 is a diagram showing an example of conventional characteristics, and FIGS. 3 and 4 are a cross-sectional view and characteristic diagram showing an example of the present invention. be. 1...P-type Si substrate, 3...gate insulating film, 4...
- Poly-Si gate, 5...diffusion layer, 6, 8... interlayer insulating film. Stone 1 Figure 2 Figures LL Su Jpla Category (set) 3 Enclosed 4 Figures

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device, comprising a step of forming a silicon oxynitride film in contact with a semiconductor substrate, and a step of patterning using an electron beam lithography method or an X-ray exposure method.